Neuroimaging studies are playing an ever more critical role in the diagnosis and management of acute stroke patients. Acute imaging is required to differentiate hemorrhage from ischemia and provides important information about the location, extent, and mechanism of cerebral injury. Neuroimaging studies also provide the only available practical and objective means of assessing brain tissue function and physiology in the acute stroke patient. Currently, head CT studies are used to select the best candidates for IV thrombolytic therapy. A growing body of evidence suggests that multimodal techniques, including diffusion-perfusion magnetic resonance imaging, may be used in the future to select patients for treatment at longer time-points. Research studies, including clinical trials for acute stroke, need the information provided by neuroimaging to triage appropriate patients and to assess outcome in a quantitative impartial fashion. The Neuroimaging Core at UCLA builds on local strengths in resources and personnel in acute stroke neuroimaging. The core will have 3 specific aims: 1) To facilitate rapid data acquisition for patients presenting with acute stroke; 2) to provide expertise in study interpretation, processing, and analysis both to assist in acute patient management and as outcome measures in the 3 Research Projects; and 3) to assist UCLA Stroke Network Hospitals in optimizing neuroimaging data acquisition and interpretation. The core will ensure that acute head computed tomography studies are immediately available 24 hrs. per day for all acute stroke patients, including radiologic expertise in study interpretation. Additionally, the core will provide 24 hrs./day availability for multimodal CT, including CT angiography and perfusion CT, multimodal MRI, including diffusion-perfusion imaging and MR angiography, ultrasound including transcranial Doppler and carotid duplex imaging, and digital subtraction angiography. The Neuroimaging Core will specifically assist the three Projects in image analysis and post-processing, including volumetric analyses. In each of these projects, neuroimaging plays a key role in study design, implementation, and outcome measures.